In known threaded closures for fuel tanks, the threaded part of the closure which projects into the fuel tank is provided with a holding lug to which a metal chain is attached. This metal chain has a free end on which an approximately X-shaped part is provided which is intended to hold the threaded closure to prevent the same from becoming lost when threadably disengaged from the fuel tank.
This metal chain often leads to a damaging of the sealing surface at the edge of the filling stub of the tank because of the friction of this chain against this edge. Thus, the chain is often clamped between the closure and the inlet stub when the threaded closure is not properly placed upon this stub. Furthermore, the known hook portion which has an approximately X-shaped configuration does not assure a reliable attachment against becoming loose because this hook-shaped part yields especially when pulling forces are applied to the threadably disengaged closure with the result that the closure and chain becomes lost.